U.S. patent number 5,306,890 [Application Number 07/710,462] was granted by the patent office on 1994-04-26 for method of producing corrugated metal sheeting and method of producing honeycomb structure therefrom for carrying catalytic agents used for purifying exhaust gases.
This patent grant is currently assigned to Nippon Steel Corporation. Invention is credited to Naoya Hamada, Akira Ishibashi, Motoi Kido, Katsuhiro Minamida, Masahi Oikawa, Atsushi Sugihashi.
United States Patent |
5,306,890 |
Minamida , et al. |
April 26, 1994 |
Method of producing corrugated metal sheeting and method of
producing honeycomb structure therefrom for carrying catalytic
agents used for purifying exhaust gases
Abstract
A method of producing a corrugated metal sheeting including a
flat metal sheet and a corrugated metal sheet joined to each other,
which sheeting is used to produce a carrier or honeycomb structure
for carrying catalytic agents used for purifying exhaust gases
from, for example, an internal combustion engine of an automobile.
In the method, the flat and corrugated metal sheets are brought
together so that corrugations of the corrugated metal sheet are
successively brought into contact with the flat metal sheet in such
a manner that the corrugated metal sheet is freely movable to
thereby release resilient stresses therefrom, and a laser beam is
incident on a contact line between the flat metal sheet and each of
the corrugations of the corrugated metal sheet, to thereby weld
them to each other.
Inventors: |
Minamida; Katsuhiro
(Sagamihara, JP), Kido; Motoi (Sagamihara,
JP), Sugihashi; Atsushi (Sagamihara, JP),
Oikawa; Masahi (Sagamihara, JP), Hamada; Naoya
(Sagamihara, JP), Ishibashi; Akira (Sagamihara,
JP) |
Assignee: |
Nippon Steel Corporation
(Tokyo, JP)
|
Family
ID: |
26476574 |
Appl.
No.: |
07/710,462 |
Filed: |
June 5, 1991 |
Foreign Application Priority Data
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Jun 5, 1990 [JP] |
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2-145479 |
Oct 18, 1990 [JP] |
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2-277893 |
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Current U.S.
Class: |
219/121.64;
219/121.82 |
Current CPC
Class: |
B23K
26/0846 (20130101); F01N 3/281 (20130101); B21D
47/00 (20130101); F01N 2330/04 (20130101); Y02A
50/2322 (20180101); F01N 2330/32 (20130101); Y02A
50/20 (20180101) |
Current International
Class: |
B23K
26/08 (20060101); B21D 47/00 (20060101); F01N
3/28 (20060101); B23K 026/00 () |
Field of
Search: |
;219/121.63,121.64,121.82,121.13,121.14,121.73,121.74,121.75
;228/173.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0011752 |
|
Jan 1984 |
|
JP |
|
0180687 |
|
Aug 1986 |
|
JP |
|
Primary Examiner: Albritton; C. L.
Attorney, Agent or Firm: Wenderoth, Lind & Ponack
Claims
We claim:
1. A method of producing a corrugated metal sheeting including a
flat metal sheet and a corrugated metal sheet joined to each other,
said method comprising the steps of:
bringing said flat and corrugated metal sheets together so that
corrugations of said corrugated metal sheet are successively
brought into contact with said flat metal sheet in such a manner
that said corrugated metal sheet is freely movable to thereby
release resilient stresses therefrom; and
making a laser beam incident on a contact line between said flat
metal sheet and each of the corrugations of said corrugated metal
sheet, to thereby weld them to each other.
2. A method as set forth in claim 1, wherein said laser beam is
deformed into a sheet-shaped laser beam having a width
corresponding to that of said flat and corrugated metal sheets, and
is focused upon said contact line.
3. A method as set forth in claim 2, wherein said laser beam is a
continuous laser beam and each of the corrugations of said
corrugated metal sheet is continuously welded to said flat metal
sheet along said contact line.
4. A method as set forth in claim 1, wherein said laser beam is
deflected along said contact line, and is focused upon said contact
line.
5. A method as set forth in claim 4, wherein said laser beam is a
continuous laser beam and each of the corrugations of said
corrugated metal sheet is continuously welded to said flat metal
sheet along said contact line.
6. A method as set forth in claim 5, wherein said laser beam is a
pulse laser beam and each of the corrugations of said corrugated
metal sheet is discretely welded to said flat metal sheet along
said contact line.
7. A method as set forth in claim 6, wherein said pulse laser beam
is obtained from a Q-switched pulse laser oscillator.
8. A method of producing a corrugated metal sheeting including a
flat metal sheet and a corrugated metal sheet joined to each other,
said method comprising the steps of:
bringing said flat and corrugated metal sheets together so that
corrugations of said corrugated metal sheet are successively
brought into contact with said flat metal sheet in such a manner
that said corrugated metal sheet is freely movable to thereby
release resilient stress therefrom; and
making a pulse laser beam incident on a contact line between said
flat metal sheet and each of the corrugations of said corrugated
metal sheet, and deflecting said laser beam therealong so that said
contact line is scanned by the deflected pulse laser beam to form
discrete welding points along said contact line, a scanning speed
of said deflected pulse laser beam being slower at side end zones
of said contact line than at a central zone thereof.
9. A method of producing a honeycomb structure from a corrugating
metal sheeting as set forth in any one of claims 1 and 8, said
method comprising:
rolling up said corrugated metal sheeting in such a manner that
corrugations of said corrugated metal sheeting are successively
brought into contact with a smooth surface of a rolled portion
obtained from said corrugated metal sheet; and
making a laser beam incident on a contact line between the smooth
surface of said rolled portion and each of the corrugations of said
corrugated metal sheeting, to thereby weld them to each other.
10. A method as set forth in claim 9, wherein said laser beam is
deformed into a sheet-shaped laser beam having a width
corresponding to that of said corrugated metal sheeting, and is
focused upon said contact line.
11. A method as set forth in claim 10, wherein said laser beam is a
continuous laser beam and each of the corrugations of said
corrugated metal sheeting is continuously welded to the smooth
surface of said rolled portion.
12. A method as set forth in claim 9, wherein said laser beam is
deflected along said contact line, and is focused upon said contact
line.
13. A method as set forth in claim 12, wherein said laser beam is a
continuous laser beam and each of the corrugations of said
corrugated metal sheeting is continuously welded to the smooth
surface of said contact line.
14. A method as set forth in claim 12, wherein said laser beam is a
pulse laser beam and each of the corrugations of said corrugated
metal sheeting is discretely welded to the smooth surface of said
rolled portion along said contact line.
15. A method as set forth in claim 14, wherein said pulse laser
beam is obtained from a Q-switched pulse laser oscillator.
Description
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to a method of producing a corrugated
metal sheeting comprising a flat metal foil or sheet and a
corrugated metal foil or sheet joined to each other, which sheeting
is used to produce a carrier or honeycomb structure for carrying
catalytic agents used for purifying exhaust gases from, for
example, an internal combustion engine of an automobile. The
invention also relates to a honeycomb structure produced from the
corrugated metal sheeting.
2) Description of the Related Art
It is well known that the honeycomb structure for carrying the
catalystic agents can be formed of a ceramic material, for example,
based upon cordierite, exhibiting a superior heat resistance.
Nevertheless, this ceramic honeycomb structure is inherently
brittle and easily broken by an impact thereof. Accordingly,
recently a metal honeycomb structure which is not brittle has been
developed and is in practical use.
The metal honeycomb structure is produced by forming a roll of a
long corrugated metal sheeting or by stacking a plurality of
honeycomb-like panels into which the corrugated metal sheeting is
cut. The corrugated metal sheeting is produced by joining a flat
metal sheet or foil and a corrugated metal sheet or foil to each
other by brazing or welding. These flat and corrugated metal sheets
may be formed of stainless steels, high-alloy corrosion-resistant
steel or the like, and may have a thickness of about from 45 .mu.m
to about 1 mm. The metal honeycomb structure produced from the
corrugated metal sheeting is received in a metal casing open at
each end, so that the honeycomb end faces of the metal honeycomb
structure are exposed from each of the openings of the metal
casing. The metal casing may be also formed of stainless steels,
corrosion-resistant high-alloy-steel or the like, and may have a
thickness of about 1 to about 2 mm. The honeycomb structure is
fixed in the metal casing by brazing or welding, and catalytic
agents are then applied to the metal honeycomb structure in a
well-known manner.
In use, the metal casing with the honeycomb structure carrying the
catalystic agents is incorporated in an exhaust system of an
internal combustion engine of an automobile, and the honeycomb
structure is subjected to severe thermal stress because it may be
exposed to wide and sudden changes of temperature, for example,
from about -25.degree. to about 900.degree. C., and thus the flat
and corrugated metal sheets must be securely joined to each other
so that they will not be separated due to the severe thermal
stress.
It is possible to securely join the flat and corrugated metal
sheets, which can endure the severe thermal stress, by brazing.
Nevertheless, the joining of the flat and corrugated metal sheets
to each other by the brazing is cumbersome and complicated, and
further the brazing per se is expensive.
Unexamined Japanese Patent Publication (KOKAI) No. 62-71547
discloses a method of producing the corrugated metal sheeting
wherein the flat and corrugated metal sheets are joined to each
other by spot-welding. In particular, the flat and corrugated metal
sheets are intermittently fed to a nip gap between a roller-shaped
electrode and a gear-shaped electrode in such a manner that the
corrugated metal sheet is engaged with the gear-shaped electrode
and the flat metal sheet is in contact with the roller-shaped
electrode. During the passage of the flat and corrugated metal
sheets between the roller-shaped and gear-shaped electrodes, which
are electrically energized, apexes of the corrugations of the
corrugated metal sheet are spot-welded to the flat metal sheet.
This method has an inherent drawback in that the production is not
efficient, i.e., the rate of production is limited because of the
intermittent feeding of the flat and corrugated metal sheets. Also,
the corrugations of the corrugated metal sheet are often subjected
to a resilient stress during the welding, because a location at
which the corrugations of the corrugated metal sheet should be
welded is restrained due to the engagement of the corrugations with
the gear-shaped electrode. Accordingly, the corrugations welded to
the flat metal sheet are often easily separated therefrom because
of the residual resilient stress, and this is, of course, further
facilitated by the severe thermal stresses.
The above-mentioned Japanese publication also discloses that the
honeycomb structure is produced by forming a roll of the corrugated
metal sheeting comprising the flat and corrugated metal sheets
spot-welded to each other, and that the roll having a honeycomb
structure is united by welding edges of the honeycomb end faces
thereof to each other, so that the roll having a honeycomb
structure will not be unrolled. Nevertheless, in use, the welded
edges may be separated from each other due to the severe thermal
stresses, because these thermal stresses tend to be concentrated at
the honeycomb end faces of the honeycomb structure, and further,
when the welded edges of the honeycomb end faces are separated from
each other, a core portion of the honeycomb structure may be
telescopically extended due to a flow pressure of the exhaust gas
and vibrations generated during the running of the automobile.
Unexamined Japanese Patent Publication (KOKAI) No. 64-40180
discloses a method of producing a honeycomb structure wherein the
flat and corrugated metal sheets are formed into a roll while being
joined to each other by resistance-welding. In particular, the flat
and corrugated metal sheets are tangentially fed to a winder at two
diametrical locations thereof in counter feed directions, and first
and second pairs of tip electrodes are transversely disposed with
respect to the flat and corrugated metal sheets, and are in contact
therewith in the vicinity of locations at which they are rolled in,
respectively. Therefore, just before the flat metal sheet is rolled
in it is welded to the rolled-in corrugated metal sheet by the
first pair of tip electrodes in contact with the flat metal sheet,
and just before the corrugated metal sheet is rolled in it is
welded to the rolled-in flat metal sheet by the second pair of tip
electrodes in contact with the corrugated metal sheet. Accordingly,
in the thus-produced honeycomb structure, the rolled-in flat and
corrugated metal sheets are welded to each other and thus cannot be
unrolled.
Nevertheless, in this production method, each of the corrugations
of the corrugated metal sheet is only welded to the flat metal
sheet at one or two local portions, and accordingly, it is
difficult to maintain the unity of the honeycomb structure under a
severe thermal stress. Of course, for example, if the first and
second pairs of tip electrodes are traversely moved step by step so
that the resistance-welding can be repeatedly carried out along
each of the corrugations of the corrugated metal sheet, it is
possible to obtain a secure joining between the flat metal sheet
and each of the corrugations, but in this case, the production rate
is very low.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a
method of producing a corrugated metal sheeting comprising a flat
metal sheet or foil and a corrugated metal sheet or foil joined to
each other, which sheeting is used to produce a carrier or
honeycomb structure for carrying catalytic agents for purifying
exhaust gases from, for example, an internal combution engine of an
automobile, wherein the flat and corrugated metal sheets can be
securely welded to each other in such a manner that any residual
resilient stress is substantially eliminated from the corrugated
metal sheet.
Another object of the present invention is to provide a method of
producing a carrier or a corrugated metal structure for carrying
the catalytic agents, which carrier is produced from the corrugated
metal sheeting, wherein a unity of the corrugated metal structure
can be ensured under any wide and sudden changes of
temperature.
In accordance with the present invention, there is provided a
method of producing a corrugated metal sheeting including a flat
metal sheet and a corrugated metal sheet joined to each other,
which comprises the steps of: bringing the flat and corrugated
metal sheets together so that corrugations of the corrugated metal
sheet are successively brought into contact with the flat metal
sheet in such a manner that the corrugated metal sheet is freely
movable to thus release resilient stresses therefrom; and making a
laser beam incident on a contact line between the flat metal sheet
and each of the corrugations of the corrugated metal sheet, to
thereby weld them to each other.
In accordance with another aspect of the present invention, there
is provided a method of producing a corrugated metal sheeting
including a flat metal sheet and a corrugated metal sheet joined to
each other, which comprises the steps of: bringing the flat and
corrugated metal sheets together so that corrugations of the
corrugated metal sheet are successively brought into contact with
the flat metal sheet in such a manner that the corrugated metal
sheet is freely movable to thereby release resilient stresses
therefrom; and making a pulse laser beam incident on a contact line
between the flat metal sheet and each of the corrugations of the
corrugated metal sheet, and deflecting the laser beam therealong so
that the contact line is scanned by the deflected pulse laser beam
to thereby form discrete welding points along the contact line, a
scanning speed of the deflected pulse laser beam being slower at
side end zones of the contact line than at a central zone
thereof.
In accordance with yet another aspect of the present invention,
there is provided a method of producing a honeycomb structure from
a corrugated metal sheeting as mentioned above, which comprises the
steps of: rolling up the corrugated metal sheeting in such a manner
that corrugations of the corrugated metal sheeting are successively
brought into contact with a smooth surface of a rolled portion
obtained from the corrugated metal sheet; and making a laser beam
incident on a contact line between the smooth surface of the rolled
portion and each of the corrugations of the corrugated metal
sheeting, to thereby weld them to each other.
BRIEF DESCRIPTION OF THE DRAWINGS
The other objects and advantages of the present invention will be
better understood from the following description, with reference to
the accompanying drawings, in which:
FIG. 1 is a schematic view of an apparatus with which a corrugated
metal sheeting production method according to the present invention
is carried out;
FIGS. 2(a), 2(b), 2(c) and 2(d) are schematic views showing how
corrugations of a corrugated metal sheet are brought into contact
with a flat metal sheet;
FIG. 3 is a partially enlarged view of the flat and corrugated
metal sheets when brought together, wherein a laser beam is
incident on a contact line between a flat metal sheet and a
corrugation of a corrugated metal sheet of FIG. 1.
FIG. 4 is a partial further enlarged view of FIG. 3;
FIG. 5 is a graph showing a relationship between a wavelength of a
laser beam and a rate of absorption at which the laser beam is
absorbed by the flat and corrugated metal sheets;
FIG. 6 is a partial perspective view showing a welding method in
which the flat and corrugated metal sheets are welded to each other
by a sheet-shaped laser beam;
FIG. 7(a) is a schematic front view showing a laser beam scanning
system;
FIG. 7(b) is a side view of FIG. 7(a);
FIG. 8(a) is a view showing an acute pulse shape of a pulse laser
beam;
FIG. 8(b) is a view showing a blunt pulse shape of a pulse laser
beam;
FIG. 9 is a schematic view showing a Q-switched laser
oscillator;
FIG. 10 is a schematic view showing a honeycomb structure
production method according to the present invention;
FIG. 11(a) is a perspective view showing a carrier or honeycomb
structure for carrying catalytic agents for purifying exhaust
gases;
FIG. 11(b) is a perspective view showing another type of carrier or
honeycomb structure for carrying catalytic agents for purifying
exhaust gases;
FIG. 12 is a side view showing another type of the corrugated metal
sheeting produced by a production method according to the present
invention;
FIG. 13 is a side view showing a modification of the corrugated
metal sheeting of FIG. 12;
FIG. 14 is a partial schematic perspective view showing a
corrugated metal sheeting produced by a production method according
to the present invention;
FIG. 15 is a schematic view of an apparatus by which a corrugated
metal sheeting production method according to the present invention
is carried out to produce the corrugated metal sheeting of FIG.
14;
FIG. 16 is a graph showing a relationship between a scanning speed
of a laser beam and a distance measured from one end of a contact
line between a flat metal sheet and a corrugation of a corrugated
metal sheet of the corrugated metal sheeting of FIG. 14;
FIG. 17 is a partially enlarged view of the flat and corrugated
metal sheets which are brought together, in which a laser beam is
incident on the flat metal sheet along the contact line between the
flat metal sheet and a corrugation of the corrugated metal sheet of
the corrugated metal sheeting of FIG. 14.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 schematically shows an apparatus for producing a corrugated
metal sheeting from a flat metal foil or sheet and a corrugated
metal foil or sheet, which sheeting is used to produce a carrier or
honeycomb structure for carrying catalytic agents for purifying
exhaust gases from, for example, an internal combustion engine of
an automobile. In this drawing, the flat and corrugated metal
sheets are indicated by references F and C, and the corrugated
metal sheeting produced therefrom is indicated by reference S. The
flat and corrugated metal sheets F and C may be formed of stainless
steels containing aluminum, high-alloy corrosion-resistant steel
(Fe-Cr-Al) or the like, and may have a thickness of about from 50
.mu.m to about 1 mm and a width of less than about 160 mm.
The production apparatus comprises a squeeze roller 10 and a
squeeze gear 12 which are freely rotatable and resiliently movable
toward each other. A nip gap between the squeeze roller 10 and the
squeeze gear 12 is defined as a welding station at which the flat
and corrugated metal sheets F and C are joined to each other by
laser-welding to produce the corrugated metal sheeting S. A pair of
guide rollers 14, 14 for guiding the flat metal sheet F to the
welding station is disposed above the squeeze roller 10 and is
spaced apart from a vertical plane extending through the nip gap
between the squeeze roller 10 and the squeeze gear 12, by a given
distance. A pair of forming gears 16, 16 for forming the corrugated
metal sheet C from a flat metal sheet material is disposed above
the squeeze gear 12 and is spaced apart from the above-mentioned
vertical plane by a given distance, and the corrugated metal sheet
C formed by the pair of forming gears 16, 16 is directed to the
welding station. With this arrangement, the flat metal and
corrugated metal sheets F and C are spread upward from the nip or
welding station between the squeeze roller 10 and the squeeze gear
12 so that a laser beam L such as a YAG laser beam, a CO.sub.2
laser beam or the like can be made incident on the welding station
to thus weld the flat and corrugated metal sheets F and C to each
other. A cylindrical lens 18 is used to focus the laser beam L on
the welding station, so that the laser energy is concentrated
thereat. Note, although the laser beam L is exaggeratedly
illustrated, it actually has a small diameter. For example, the YAG
laser beam has a diameter of from about 6 to about 10 mm before it
is incident on the cylindrical lens 18, and has a focused diameter
of from about 0.5 to about 3 mm in a zone of the depth of focus. A
drive roller 20 and a drive gear 22 are disposed just below the
squeeze roller 10 and the squeeze gear 12, and are engaged with the
flat and corrugated sides of the corrugated metal sheeting S,
respectively. As apparent from FIG. 1, the drive roller 20 and the
drive gear 22 are driven by a suitable drive source (not shown) to
move the corrugated metal sheeting S downward, so that the flat and
corrugated metal sheets F and C are pulled into the nip gap or
welding station between the squeeze roller 10 and the squeeze gear
12, and then brought together thereat.
The welding is carried out in such a manner that each of the
corrugations of the corrugated metal sheet C is joined to the flat
metal sheet F at the apex thereof. To this end, the laser beam L is
preferably focused by the cylindrical lens 18 on a squeeze location
24 (FIG. 2(a)) at which a contour line 26 described by the teeth of
the squeeze gear teeth 12 is in contact with the squeeze roller 10,
because the apexes of the corrugations of the corrugated metal
sheet C must be successively brought into contact with the flat
metal sheet F at the squeeze location 24 while the flat and
corrugated metal sheets F and C are pulled into the welding
station. Thus, the location at which a contact between the apex of
the corrugation and the flat sheet metal sheet F occurs can be
irradiated by the focused laser beam L so that the materials are
melted and the apex of the corrugation thus joined to the flat
metal sheet by the welding.
In practice, however, all of the corrugations of the corrugated
metal sheet C are not always in contact with the flat metal sheet F
at the squeeze location 24, because of the clearances maintained
between the corrugations of the corrugated metal sheet C and the
teeth of the squeeze gear 12 so that the corrugated metal sheet C
is freely movable to thus release resilient stresses therefrom at
the welding station. Namely, the corrugation of the corrugated
metal sheet C may be in contact with the flat metal sheet F at a
location other than the squeeze location 24, as shown in FIGS. 2(b)
and 2(c), and further, the two adjacent corrugations thereof may be
in contact with the flat metal sheet F at both sides of the squeeze
location, as shown in FIG. 2(d).
In the cases as shown in FIGS. 2(b) and 2(c), for example, when the
corrugations of the corrugated metal sheet C have a pitch of about
2.5 mm, a maximum distance (l.sub.1, l.sub.2) by which the
corrugation is offset from the squeeze location 24 is about
.+-.1.25 mm. Accordingly, the focused laser beam L must have a
depth of focus which is more than the maximum offset range (l.sub.1
+l.sub.2) before a proper welding can be ensured in the cases as
shown in FIGS. 2(b) and 2(c). Nevertheless, according to the
present invention, the depth of focus may be less than the maximum
offset range (l.sub.1 +l.sub.2), because the laser energy can be
concentrated at the location of the contact between the apex of the
corrugation and the flat metal sheet F. In particular, for example,
FIG. 3 shows a case similar to FIG. 2(c), in which a corrugation
C.sub.1 of the corrugated metal sheet C is in contact with flat
metal sheet F below the squeeze location 24. In this case, the
laser beam L introduced into a V-shaped space defined by the
corrugation C.sub.1 and the flat metal sheet F can be converged by
reflections at the location of the contact between the apex of the
corrugation C.sub.1 and the flat metal sheet F, as shown in FIG. 4.
The same holds true for the cases as shown in FIGS. 2(b) and 2(d).
Thus, according to the present invention, the depth of focus of the
focused laser beam L can be virtually expanded so that the welding
between the apexes of the corrugations and the flat metal sheet F
can be securely and continuously carried out. For example, where
the cylindrical lens 18 has a focal distance of 75 mm, the focused
laser beam L may have a virtual depth of focus of .+-.1.25 mm.
Also, this means that a cumbersome optical adjustment needed for
exactly focussing the laser beam L on the squeeze location 24
becomes unnecessary. Namely, the focus of the laser beam L can be
relatively misaligned with the squeeze location 24.
While the laser beam L is reflected in the V-shaped space defined
by the flat metal sheet F and the corrugation of the corrugated
metal sheet C, a part of the laser energy is absorbed by the
materials of the metal sheets. The rate of absorption of the laser
energy varies in accordance with a wavelength of the laser beam
used, because the material surfaces of the metal sheets have a
light absorption characteristic which is dependent on a wavelength
of the laser beam. For example, in the light absorption
characteristic as shown in FIG. 5, a YAG laser beam having a
wavelength of 1.06 .mu.m has a reflectivity of about 60%
(=1-.gamma.), and a CO.sub.2 laser beam having a wavelength of 10.6
.mu.m has a refectivity of about 90%. Although the CO.sub.2 laser
beam exhibits an energy concentration superior to that of the YAG
laser beam, this does not exclude the use of YAG laser in the
application of the present invention.
To ensure that each of the corrugations of the corrugated metal
sheet C is transversely and longitudinally welded to the flat metal
sheet F, the laser beam L may be deformed into a sheet-like shape
having a width corresponding to that of the metal sheets F and C,
as shown in FIG. 6. Namely, the sheet-shaped laser beam L is
focused by the cylindrical lens 18 on the contact line between the
flat metal sheet F and the corrugation of the corrugated metal
sheet C, and thus the welding is transversely and continuously
carried out therealong. Note, the deformation of the laser beam
into the sheet-like shape is performed by using, for example, an
integration mirror, as is well-known in this field.
Alternatively, the laser beam L may be irradiated to the contact
line between the flat metal sheet F and the corrugation of the
corrugated metal sheet C by a suitable optical scanning system, as
shown in FIGS. 7(a) and 7(b), which includes a reflector 28
disposed above the cylindrical lens 18 and having a slanted
cylindrical reflecting surface 30, and a polygon mirror 32 disposed
beside a space between the reflector 28 and the cylindrical lens 18
so that the laser beam L made incident thereon is reflected from
the polygon mirror 32 toward the slanted cylindrical reflecting
surface 30. With this arrangement of the optical scanning system,
the contact line between the flat metal sheet F and the corrugation
of the corrugated metal sheet C is scanned with the deflected and
focused laser beam L, so that the corrugation of the corrugated
metal sheet C can be transversely welded to the flat metal sheet
F.
The laser beam L may be a pulse laser beam so that the welding is
discretely carried out along the contact line between the flat
metal sheet F and the corrugation of the corrugated metal sheet C.
Where at least one of the flat and corrugated metal sheets F and C
is relatively thin, preferably an acute pulse shape having a
relatively narrow width is given to the pulse laser beam. Namely,
the pulse laser beam L should have an acute pulse shape as shown in
FIG. 8(a) rather than a blunt pulse shape as shown in FIG. 8(b).
This is because an amount of thermal energy irradiated at the
welding point by the acute pulse laser beam is smaller than that of
the blunt pulse laser beam. In particular, an amount of thermal
energy irradiated at the welding point by the blunt pulse laser
beam is larger, and a time for which the thermal energy is
irradiated at the welding point thereby is longer, and thus the
material of the thin metal sheet or foil may be excessively melted
to a point that a hole is formed therein. Conversely, although the
acute pulse laser beam of FIG. 8(a) has a higher peak than that of
the blunt pulse laser beam of FIG. 8(b), an amount of thermal
energy irradiated at the welding point by the acute pulse laser
beam is smaller, and a time for which the thermal energy is
irradiated at the welding point is shorter, and thus the material
of the thin metal sheet or foil cannot be excessively melted and a
proper welding can be safely carried out.
The acute pulse laser beam as mentioned above may be obtained by,
for example, a well-known Q-switched CO.sub.2 laser oscillator as
shown in FIG. 9. This laser oscillator comprises a resonace tube 34
having a half mirror 36 and a reflector 38 disposed at the ends
thereof, an electric CO.sub.2 gas-discharging tube 40 disposed
within the resonace tube 34 near the reflector 38, a pair of convex
lenses 42, 42 disposed within the resonace tube 34 such that there
is a common focal point therebetween, and an optical chopper 44
allowing and shutting off a passage of light at a given frequency.
While the optical chopper 44 is closed, CO.sub.2 is excited from
the ground level to a certain energy level, and while the optical
chopper 44 is opened, a light generated in the discharging tube 40
is oscillated and amplified between the half mirror 36 and the
reflector 38, whereby the acute pulse laser beam as shown in FIG.
8(a) can be output from the half mirror 36.
As apparent from the foregoing, according to the present invention
a welding can be carried out in such a manner that resilient stress
can be released from the corrugated metal sheet C, because the
corrugated metal sheet C is freely movable, to thus release
resilient stress therefrom at the welding station, due to the
clearances between the corrugations of the corrugated metal sheet C
and the teeth of the squeeze gear 12. This is a significant feature
of the present invention, because the residual resilient stresses
can be substantially eliminated from the finished corrugated metal
sheeting S shown in FIG. 1, and thus the corrugations welded to the
flat metal sheet do not have a tendency to separate from each toher
due to the residual resilient stresses.
FIG. 10 shows a method of producing the honeycomb structure from
the corrugated metal sheeting S produced by the method shown in
FIG. 1. The corrugated metal sheet S is fed through a guide roller
46 and a guide gear 48, and is then rolled up by a suitable winder
shaft 50 driven by an electric motor 52 (symbolically illustrated).
As shown in FIG. 10, while the corrugated metal sheeting S is
rolled up, the corrugations of the corrugated metal sheeting S are
successively welded to a smooth surface of the rolled portion R by
a laser beam L', such as a YAG laser beam, a CO.sub.2 laser beam or
the like, in substantially the same manner as mentioned above.
Namely, the laser beam L' is focused by a cylindrical lens 18' on a
location at which each of the corrugations of the corrugated metal
sheeting S is brought into contact with the smooth surface of the
rolled portion R to form a V-shaped space therebetween, and thus
the welding can be carried out in substantially the same manner as
mentioned above. Note, the winder shaft 50 is movable in the two
directions indicated by an arrow 54, and as a radius of the rolled
portion R is increased, it is controlled to move in one of two
directions (i.e., right in FIG. 10) so that the laser beam L' can
be always made incident on the location at which each of the
corrugations of the corrugated metal sheeting S is in contact with
the smooth surface of the rolled portion R.
As shown in FIG. 11(a), the honeycomb structure thus-produced is
received in a cylindrical metal casing 56 having an opening at each
end thereof, such that the honeycomb end faces of the honeycomb
structure are exposed from these openings. The cylindrical metal
casing 56 may be formed of stainless steels, corrosion-resistant
high-alloy-steel or the like, and may have a thickness of about 1
to about 2 mm. The honeycomb structure is fixed in the cylindrical
metal casing 56 by a conventional welding method, and catalytic
agents are then applied to the metal honeycomb structure in a
well-known manner. Further, the honeycomb structure may be produced
by stacking a plurality of honeycomb panels into which the
corrugated metal sheeting S is cut; these stacked honeycomb panels
are joined by a conventional welding method, and then received in a
box-like metal casing 58 having an opening at each side thereof, as
shown FIG. 11(b). The box-like metal casing 58 may be also formed
of the same material as the cylindrical metal casing 56. Similarly,
the stacked honeycomb panels or honeycomb structure is fixed in the
box-like metal casing 58, and the catalytic agents are then applied
to the metal honeycomb structure in a well-known manner.
When the honeycomb structure is constructed from the honeycomb
panels, these honeycomb panels may be obtained from a corrugated
metal sheeting as shown in FIG. 12, in which a corrugated metal
sheet C is sandwiched by two flat metal sheets F, and which can be
produced in substantially the same manner as mentioned above. FIG.
13 shows a modification of the corrugated metal sheeting of FIG.
12, in which an angularly corrugated metal sheet AC is substituted
for the corrugated metal sheet C.
As schematically shown in FIG. 14, when the welding is discretely
carried out along the contact line between the flat metal sheet F
and the corrugation of the corrugated metal sheet C, i.e., when a
plurality of welding points WP are formed along the contact line
therebetween, preferably the pitches of the welding points WP are
closer to each other at the side end zones 60, 60 of the contact
line than at a central zone 62 thereof. This is because, when the
honeycomb structure is produced from the corrugated metal sheeting
and is used as the carrier for the catalytic agents for purifying
the exhaust gases, the corrugations are more easily separated from
the flat metal sheet F at the side end zones 60, 60 than at the
central zone 62 thereof, because the severe thermal stress has a
tendency to be concentrated at the side end zones 60, 60.
FIG. 15 schematically shows an apparatus for producing the
corrugated metal sheeting as shown in FIG. 14. In this drawing, the
same references as in FIG. 1 represent the same elements. This
production apparatus features a galvano-mirror 64 by which the
laser beam L is deflected at a variable speed. In particular, the
contact line between the flat metal sheet F and the corrugation of
the corrugated metal sheet C is scanned with the deflected laser
beam L so that the scanning speed is varied as shown in a graph of
FIG. 16 (Note, the abscissa thereof represents a distance measured
from one end of the contact line). As apparent from this graph, the
scanning speed is slower at the side end zones 60, 60 than at the
central zone 62, and thus a discrete welding can be carried out as
shown in FIG. 14. It is possible to control the scanning speed, as
shown in the graph of FIG. 16, by energizing a drive circuit (not
shown) for the galvano-mirror 64 with a voltage which is varied to
be analogous to the characteristic of FIG. 16. When only the
discrete welding as mentioned above is desired, the laser beam L
may be made incident on the flat metal sheet F along the contact
line, as shown in FIG. 17.
The present invention was actually embodied as shown in the
following examples:
EXAMPLE I
(1) Flat and corrugated sheets having a width of 120 mm were
obtained from ferrite type stainless steel sheets containing 15% Cr
and 4.5% Al and having a thickness of 50 .mu.m.
(2) A corrugated sheeting was produced from these flat and
corrugated sheets according to the production method as shown in
FIG. 1, by using a normal pulse YAG laser beam (100 pps) having a
pulse energy of 200 mJ. The rate of production was 10 m/min.
(3) A honeycomb structure was produced from this corrugated
sheeting according to the production method as shown in FIG. 10, by
using the same normal pulse YAG laser beam as in the production of
the corrugated sheeting. The rate of production was 10 m/min.
(4) The honeycomb structure thus-produced was received in a
cylindrical casing made of SUS 304 stainless steel (AISI 304), to
thereby obtain a metal carrier as shown FIG. 11(a).
(5) For testing, the metal carrier was incorporated in an exhaust
gas system for an internal combution engine, and was maintained at
a temperature of 850.degree. C. over a period of 300 hours. No
damage thereto was found, and further, the core portion of the
honeycomb structure was not telescopically extended.
EXAMPLE II
(1) Flat and corrugated sheets having a width of 100 mm were
obtained from ferrite type stainless steel sheet containing 15% Cr
and 4.5% Al and having a thickness of 50 .mu.m.
(2) A corrugated sheeting was produced from these flat and
corrugated sheets according to the production method as shown in
FIG. 1, by using a sheet-shaped CO.sub.2 laser beam (1 kW) having a
width of 100 mm, and a cylindrical lens having a focal distance of
75 mm. The rate of production was 7 m/min.
(3) A honeycomb structure was produced from this corrugated
sheeting according to the production method as shown in FIG. 10, by
using the same sheet-shaped CO.sub.2 laser beam as in the
production of the corrugated sheeting. The rate of production was 7
m/min.
(4) The honeycomb structure thus produced was received in a
cylindrical casing made of SUS 304 stainless steel (AISI 304), to
thereby obtain a metal carrier as shown FIG. 11(a).
(5) The metal carrier was tested under the same conditions as in
EXAMPLE I. No damage thereto was found, and further, the core
portion of the honeycomb structure was not telescopically
extended.
EXAMPLE III
(1) Flat and corrugated sheets having a width of 120 mm were
obtained from ferrite type stainless steel sheet containing 15% Cr
and 4.5% Al and having a thickness of 50 .mu.m.
(2) A corrugated sheeting was produced from these flat and
corrugated sheets according to the production method as shown in
FIG. 1, by using a CO.sub.2 pulse laser beam (12 kHz) obtained from
a laser oscillator (as shown in FIG. 9) and having a pulse energy
of 200 mJ. The rate of production was 15 m/min.
(3) A honeycomb structure was produced from this corrugated
sheeting according to the production method as shown in FIG. 10, by
using the same CO.sub.2 pulse laser beam as in the production of
the corrugated sheeting. The rate of production was 15 m/min.
(4) The honeycomb structure thus produced was received in a
cylindrical casing made of SUS 304 stainless steel (AISI 304), to
thereby obtain a metal carrier as shown FIG. 11(a).
(5) The metal carrier was tested under the same conditions as in
EXAMPLE I. No damage thereto was found, and further, the core
portion of the honeycomb structure was not telescopically
extended.
EXAMPLE IV
(1) Flat and corrugated sheets having a width of 120 mm were
obtained from ferrite type stainless steel sheet containing 15% Cr
and 4.5% Al and having a thickness of 100 .mu.m.
(2) A corrugated sheeting was produced from these flat and
corrugated sheets according to the production method as shown in
FIG. 1, by using a CO.sub.2 pulse laser beam (12 kHz) obtained from
a laser oscillator (as shown in FIG. 9) and having a pulse energy
of 200 mJ, and a cylindrical lens having a focal distance of 75 mm.
The rate of production was 10 m/min.
(3) A honeycomb structure was produced from this corrugated
sheeting according to the production method as shown in FIG. 10, by
using the same CO.sub.2 pulse laser beam as in the production of
the corrugated sheeting. The rate of production was 10 m/min.
EXAMPLE V
(1) Flat and corrugated sheets having a width of 120 mm were
obtained from ferrite type stainless steel sheet containing 15% Cr
and 4.5% Al and having a thickness of 50 .mu.m.
(2) A corrugated sheeting was produced from these flat and
corrugated sheets according to the production method as shown in
FIG. 1, by using a normal pulse YAG laser beam (100 pps) having a
pulse energy of 200 mJ and by deflecting the laser beam at the
variable scanning speed shown in FIG. 16.
(3) A honeycomb structure was produced from this corrugated
sheeting according to the production method as shown in FIG. 15, by
using the same normal pulse YAG laser beam as in the production of
the corrugated sheeting and by deflecting the laser beam at the
same variable scanning speed.
(4) The honeycomb structure thus produced was received in a
cylindrical casing made of SUS 304 stainless steel (AISI 304), to
thereby obtain a metal carrier as shown FIG. 11(a).
(5) For testing, the metal carrier was incorporated in an exhaust
gas system for an internal combution engine of 3000 cc, and was
maintained at a temperature of 850.degree. C. over a period of 400
hours. No damage thereto was found, and further, the core portion
of the honeycomb structure was not telescopically extended.
Finally, it will be understood by those skilled in the art that the
foregoing description is of preferred embodiments of the disclosed
method, and that various changes and modifications may be made to
the present invention without departing from the spirit and scope
thereof.
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